A book of sermon illustrations can be useful when you need ideas about how to provide an anecdote that illustrates a point that you are making.
1001 Illustrations That Connect by 
More Movie-Based Illustrations for Preaching and Teaching by 
1001 Quotations That Connect by You'll find books in the BV 4211 section that deal with how to prepare a sermon. Some books will give you tips on how to connect with different audiences and some will focus on crafting different types of sermons.
Preaching to a Postmodern World by 
The 12 Essential Skills for Great Preaching - Second Edition by 
Preparing Expository Sermons by Reading a sermon can provide you with good ideas for your sermon. The BV section has collections of sermons from a variety of different preachers, and the BX section will have collections of sermons by an individual preacher.
American Sermons (LOA #108) by 
Best Sermons Ever (Compact Edition) by 
20 centuries of great preaching; an encyclopedia of preaching by 
Treasury of the World's Great Sermons by 
John Wesley's Sermons by 
